The events of Sep. 11, 2001 instigated an urgency for more effective and stringent screening of airport baggage. The urgency for security expanded from an inspection of carry-on bags for knives and guns to a complete inspection of checked bags for a range of hazards with particular emphasis upon concealed explosives. X-ray imaging is a widespread technology currently employed for screening. In an X-ray imaging system, an X-ray source transmits X-rays towards a detector and the detector detects the X-rays to identify a set of materials.
Identification systems based on X-ray diffraction (XRD) techniques provide an improved discrimination of the materials compared to that provided by the X-ray imaging system. The XRD identification systems also include the detector and measure d-spacings between lattice planes of micro-crystals in materials. A “d-spacing” is a perpendicular distance between adjacent lattice planes in any of the materials.
However, the XRD identification systems suffer from degradation effects on a signal detected by the detector. The effects are created by self-attenuation of diffracted X-rays by an item, such as a bag, under investigation. If these degradation effects are not reduced, a threat material within the item may be difficult to identify and the difficulty in identification leads to a false alarm rate in identifying the threat material.